Browsing by Subject "Proton conductivity"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Open Access Lyotropic liquid crystalline (LLC) phosphoric acid-10-lauryl ether: mesophases, proton conductivity and synthesis of transparent mesoporous hydroxyapatite thin films(Bilkent University, 2014-06) Tunkara, EbrimaMany salts, acids, and bases with low deliquescence relative humidity (DRH) can organize non-ionic surfactants into lyotropic liquid crystalline (LLC) mesophases that form a ready platform for the synthesis of mesoporous materials. In this study, we show that phosphoric acid (H3PO4, PA) with low DRH value can also be used as a solvent in assembling non-ionic surfactant (C12H25(OCH2CH2)10OH, C12EO10) into stable LLC mesophases within a broad range of composition (the concentration can be as high as 20 PA/C12EO10 mole ratio). The PA/C12EO10 mesophase is bi-continuous cubic phase (V1) in extremely low concentrations (2 PA/C12EO10 mole ratio), 2D/3D hexagonal phases (H1) at moderate compositions (3 to 5 PA/C12EO10 mole ratio) and micelle cubic (I1) at high, (more than 5) H3PO4/C12EO10 mole ratios, with a typical unit cell parameter of 127, 55, and 116 Å, respectively. The mesophases of the lower concentrated samples (less than 15 mole ratio) have high thermal stability, with melting points greater than 120 oC. However the melting point drops to less than 50 oC for extremely high concentrations (more than 17 PA/C12EO10 mole ratio). The LLC mesophases were also found to exhibit high proton conductivities (~10-3 S/cm) at room temperature. The proton conductivities were even higher (10-2 S/cm) at some elevated temperatures and reduced to (10-4 S/cm) at temperatures less than 0oC. The conductivity in the cubic phase is slightly higher. Both the temperature and composition-dependent conductivity obey the most accepted proton conductivity mechanisms: Grotthuss and Vehicle. We went further to show that the combination of H3PO4 and another low DRH species, such as Ca(NO3)2·4H2O also form stable mesophases; without precipitating salts, under a wide range of concentration, from 5.3/1 to 13.3/1 precursor to surfactant ratio. High acidity stabilizes both the aqueous solution as well as the LLC phases. The clear solutions obtained from the precursor-surfactant mixtures were spin coated on glass substrates (as thin as a few hundred nanometers) and calcined to form transparent nano-size mesoporous hydroxyapatite (HAp) thin films. The formation of semi-crystalline HAp in our synthetic approach is not a straight forward process; it involves the formation of some intermediate products and also requires a calcination temperature of at least 300 oC. The formation, which starts at 300 oC, is preceded by the evaporation of nitric acid and excess water molecules to the surrounding. The crystallization continues at 400 oC and completes at 500 oC, keeping the uniformity, porosity, and transparency of the films. Films of the 5.3/1 ratio, calcined at 300 oC have high surface area of up to 96 m2/g, which dropped down to 20 m2/g at 500 oC. The mesopores start collapsing at around 600 oC. The pore size, pore walls, and the pore volumes were obtained from the N2 sorption measurements and the values are 22.4 nm, 10 nm, and 0.58 cm3/g, respectively. We also investigated the effect of precursor concentration on both the pore sizes, as well as the thicknesses of the pore walls. The results showed a reduction of surface area, and also narrower pore size distribution with increasing concentration. Temperature was also observed to have the same effect on crystallinity in all the compositions studied. All the investigations on these two systems were carried out using XRD (X-ray diffraction), FT-IR (Fourrier Transform Infrared Spectroscopy), Raman spectroscopy, POM (Polarized Light Optical Microscope), N2-sorption measurements, PEIS (Potentiostatic Electrochemical Impedance Spectroscopy), TEM (Transition Electron Microscopy), SEM (Scanning Electron Microscopy) etc.Item Open Access Strong acid-nonionic surfactant lyotropic liquid-crystalline mesophases as media for the synthesis of carbon quantum dots and highly proton conducting mesostructured silica thin films and monoliths(American Chemical Society, 2015) Olutaş, E. B.; Balcı, F. M.; Dag, Ö.Lyotropic liquid-crystalline (LLC) materials are important in designing porous materials, and acids are as important in chemical synthesis. Combining these two important concepts will be highly beneficial to chemistry and material science. In this work, we show that a strong acid can be used as a solvent for the assembly of nonionic surfactants into various mesophases. Sulfuric acid (SA), 10-lauryl ether (C12E10), and a small amount of water form bicontinuous cubic (V1), 2Dhexagonal (H1), and micelle cubic (I1) mesophases with increasing SA/ C12E10 mole ratio. A mixture of SA and C12E10 is fluidic but transforms to a highly ordered LLC mesophase by absorbing ambient water. The LLC mesophase displays high proton conductivity (1.5 to 19.0 mS/cm at room temperature) that increases with an increasing SA content up to 11 SA/ C12E10 mole ratio, where the absorbed water is constant with respect to the SA amount but gradually increases from a 2.3 to 4.3 H2O/C12E10 mole ratio with increasing SA/C12E10 from 2 to 11, respectively. The mixture of SA and C12E10 slowly undergoes carbonization to produce carbon quantum dots (c-dots). The carbonization process can be controlled by simply controlling the water content of the media, and it can be almost halted by leaving the samples under ambient conditions, where the mixture slowly absorbs water to form photoluminescent c-dot-embedded mesophases. Over time the c-dots grow in size and increase in number, and the photoluminescence frequency gradually shifts to a lower frequency. The SA/C12E10 mesophase can also be used as a template to produce highly proton conducting mesostructured silica films and monoliths, as high as 19.3 mS/cm under ambient conditions. Aging the silica samples enhances the conductivity that can be even larger than for the LLC mesophase with the same amount of SA. The presence of silica has a positive effect on the proton conductivity of SA/C12E10 systems.